Blue print coating



Patented Sept. 5, 1939 UNITED STATES PATENT orrlca BLUE rnmr COATIINGGarnet Philip Ham, Old Greenwich, Conn assignor to American CyanamidCompany, New York, N. Y a corporation of Maine No Drawing. ApplicationMay 20, 1939, Serial No. 274M39- 7 Claims.

Serial No. 219,599, filed July 16, 1938, now Pat ent No. 2,165,166, July4, 1939.

Blue print coatings in general consist of a light sensitive ferric salt,a ferricyanide, and other substances which may be necessary to producethe desired solution pH. In general in the past, potassium ferricyanidehas been standard as the ferricyanide component of blue print coatings,and ferric ammonium oxalate has been used where fast printing coatingshave been desired, other ferric salts such as the citrate being usedwhere slower speed is unobjectionable.

According to the present invention, certain sensitizers are added to theblue print coating which increase the printing speed of the coating anddo so without any-sacrifice in latitude but with an actual increase inlatitude so that in spite of very greatly increased printing speeds,practically pure white backgrounds can be readily obtained which is animportant factor in the reproduction of line drawings, the mostimportant single use for. blue print paper. These sensitizers arecompounds of strong organic bases consisting of quaternary ammoniumcompounds. Among the quaternary ammonium compounds included in theinvention, two have proven to be of particular effectiveness, namely,tetramethylammonium hydroxide and trimethylbenzylammonium hydroxide.

I have found that the effectiveness of the sensitizers of the presentinvention varies to a considerable extent with the relative amount ofsensitizer and -ferricyanide component in the coating. The improvedeffect does not continue to increase with increased amounts ofsensitizers but passes through a maximum, thereafter declining so thatboth very small amounts of sensitizer and very large amounts ofsensitizer give results which are relatively poor ascompared to. thoseobtainable within the optimum range. This range is not critical; Goodresults are obtained with an amount of the sensitizer stoichiometricallycorresponding to the total ferricyanide present. Results are improvedwith the addition of somewhat larger amounts of sensitizer, and amaximum is reached in most cases when the amount of sensitizer isstoichiometrically equivalent to twice the total ferricyanide present inthe coating. Additional amounts of sensitizer result in a lowering ofactivity and therefore, while (Cl. 9H)

the invention in its broader aspects is not limited to a particularproportion of sensitizer, in more specific aspect a proportion ofsensltizer approximately twice the stoichioznetrical equivalent offerricyanide component is included as a specific preferred modificationof the invention.

When blue print coatings containing a ferrocyanide, to replace a portionof ferricyanide generally employed, and used with a sensitizer theprinting speed andlatitude are increased but the 10 keeping qualities ofthe paper are decreased.

I havenot as yet been able to determine the mechanism by which thesensitizers operate, and the present invention is not intended to belim-' ited to any theory of action. I do believe, however, that there issome chemical relationship between the sensitizer and the iron-cyanogencomplex, and this is advanced as a probable explantion of the operationof the present invention without in any way limiting it thereto.

It is an advantage of the present invention .that the addition ofsensitizers increases both speed and latitude of blue print coatingscontaining either potassium or sodium ferricyanide alone, or mixtures ofsodium ferricyanide and sodium ferrocyanide. I have found that optimumresults are, however, obtained when strongly basis sensitizers such asthe quaternary ammonium hydroxides or their salts with weak'acids areused. Other quaternary ammonium compounds such as the quaternaryammonium sulfates, alkyl sulfates, chloratesl nitrates, halides, etc.,may be used as sensitizers' in blue printing compositions as thehydroxyl group does not appear to be the essential group. The increasein latitude is particularly effective in cases where otherwise theprinting speed sometimes results in slightly colored backgrounds. I havenot as yet been able to determine the reason for the extraordinarylatitude combined withhigh speed 40 which is obtained with the best ofthe sensitizers of the present invention. This is an unusual resultsince normally factors which increase printing speed decrease latitudeand cause trouble with backgrounds and, while we have at present noproven explanation for this extraordinary behaviour of the sensitizersof the present invention, it constitutes one of their most importantadvantages since all of the desirable results of high speed printing areobtained without any compromise on background quality.

The invention will be described in greater detail in conjunction withthe following specific examples which illustrate typical embodiments ofthe present invention which, however, is not limited to the detailstherein set forth and particularly is not limited to the illustrativecompounds of the strong organic bases therein described.

Solution B is added to Solution A at a temperature of approximately 35to 40 C., the addition being in the absence of actinic light and withsufficient agitation to ensure thorough mixture. ll parts oftrimethylbenzylammonium hydroxide are then added and the entire solutioncooled to C., whereupon 0.5 part citric acid is introduced. The finalsolution has a pH of approxl-;

mately 7.6 and may be used for coatingpaper at room temperatureorslightly elevated temperatures, all steps, of course, being in theabsence" of 'actinic light. The paper was compared with a premium paperof high speed printing characteristics using conditions of machineprinting corresponding to the CF Pease #20 continuous blue printingmachine. The blue intensity at 6 seconds exposure (15 feet per minute)was almost Y of the same depth as on the premium paper at 42 secondsexposure (2 feet per minute). Normal fast running is 10 feet per minute.Pure white backgrounds were obtained, and the coating showed highquality for the reproduction of line drawings and was also suitable forcontact printing from negatives giving pictures of good detail. At thehighest machine speeds at which the above machine can run (about 19 feetper minute), the blues were still of satisfactory depth for goodreproduction of line drawings and were notably deeper than the premiumgrade commercial paper at the same speed.

Example, 2 L Two solutions were prepared as follows:

" Solution A Water 50 Ferric ammonium oxalate 20 Potassium oxalate 2.5Solution B Water 37 Sodium ferricyanide (in liquor) '8 Sodiumferrocyanide 2.83

In Solution B the normal ferricyanide liquor which containsapproximately 1.33% sodium ferrocyanide has been enriched withadditional sodium ferrocyanide. Solution B is added to Solution A asdescribed in Example 1, then 24 parts of a 10% solution oftetramethylammonium hydroxide is introduced, the solution cooled and 1-part of citric acid added to give a pH of approxiv hfl 6.25. Thesolution is then ready for coat- Example 3 A solution was made up as inExample 2 except the amount of citric acid was reduced by 50%.

The paper produced was not materially afl'ected by the reductionof acidand the results obtained compare favorably with those of Examples 1 and2. In diret'comparison with other coating formulae, it is definitelyshown to be superior'for Solution B is added to Solution A as describedin Example 1, then 2 parts of trimethylbenzylammonium hydroxide isintroduced, the'solution cooled and 1 part of citric acid added.

The paper produced, using this coating composition, was not quite asfast as that of Example l, but the keeping qualities are much better,and

otherwise compares favorably with the better gradesof commercial paper.

What I claim is:

1. A blue print coating composition comprising a light sensitive ferricsalt, a soluble ferricyanide, and a quaternary ammonium compound in aneflective amoun 2. A blue print coating composition comprising a lightsensitiveferric salt, a soluble ferricyanide and trimethylbenzylammoniumhydroxide in an effective amount.

3. A blue print coating composition comprising a light sensitive ferricsalt, a soluble ferricyanide and tetramethylammonium hydroxide in aneffective amount.

4. A blue print coating composition according to claim 1 in which thequaternaryammonium compound is stoichiometrically equivalent toapproximately twice the ferricyanide.

. 5. A blue print coating composition comprisin a light sensitive ferricsalt, a soluble ferrlcyanide and a strongly basic quaternary ammoniumcompound in an eflective amount.

6. A blue print coating composition according to claim 2 in which thetrimethylbenzylammonlum hydroxide is stoichiometrically equivalent toapproximately twice the ferricyanide.

'7. A blue print coating composition according to claim '3 in which thetetramethylammonium hydroxide is stoichiometrically equivalent toapproximately twice the ferricyanlde.

GARNET PHILIP HAM.

